class Snake {
  head: HTMLElement;
  bodies: HTMLCollection;
  element: HTMLElement;

  constructor() {
    this.element = document.getElementById('snake')!;
    this.head = document.querySelector('#snake > div') as HTMLElement;
    this.bodies = document.getElementById('snake')!.getElementsByTagName('div');
  }

  get X() {
    return this.head.offsetLeft
  }
  get Y() {
    return this.head.offsetTop
  }

  set X(value: number) {
    if (this.X === value) {
      return
    } else if (value < 0 || value > 290) {
      throw new Error('蛇撞墙了！')
    }

    if (this.bodies[1] && (this.bodies[1] as HTMLElement).offsetLeft === value) {
      if (value > this.X) {
        value = this.X - 10;
      } else if (value < this.X) {
        value = this.X + 10
      }
    }

    this.moveBody()
    this.head.style.left = value + 'px'
    this.checkHeadBody();
  }
  set Y(value: number) {
    if (this.Y === value) {
      return
    } else if (value < 0 || value > 290) {
      throw new Error('蛇撞墙了！')
    }

    if (this.bodies[1] && (this.bodies[1] as HTMLElement).offsetTop === value) {
      if (value > this.Y) {
        value = this.Y - 10;
      } else if (value < this.Y) {
        value = this.Y + 10
      }
    }

    this.moveBody()
    this.head.style.top = value + 'px'
    this.checkHeadBody();
  }

  addBody() {
    this.element.insertAdjacentHTML("beforeend", "<div></div>")
  }

  moveBody() {
    for (let i = this.bodies.length - 1; i > 0; i--) {
      let X = (this.bodies[i - 1] as HTMLElement).offsetLeft;
      let Y = (this.bodies[i - 1] as HTMLElement).offsetTop;

      (this.bodies[i] as HTMLElement).style.left = X + 'px';
      (this.bodies[i] as HTMLElement).style.top = Y + 'px';
    }
  }

  checkHeadBody(){
    for(let i=1;i<this.bodies.length;i++){
      let bd = this.bodies[i] as HTMLElement
      if(this.X === bd.offsetLeft && this.Y === bd.offsetTop){
        throw new Error('蛇头撞到自己了！')
      }
    }
  }
}

export default Snake;